The present invention generally relates to electrophotographic printing devices and more specifically to the reduction or elimination of toner leakage through seals that are used in printer toner cartridges.
Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices, such as laser printers and copiers, use toner particles to form the desired image on the print medium, which is usually some type of paper. Once the toner is applied to the paper, the paper is advanced along the paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner is fused to the paper through a process of heat and pressure.
FIG. 1 is a diagram of typical laser printing device 100 employing an Electro Photography (EP) process. Laser printing device 100 employs a removable toner cartridge 118 configured to supply toner particles to an integral Organic Photo Conductor (OPC) drum 109 which applies a developed toner image to a receiving media, e.g., a sheet of paper. For monochromatic printing, a single color of toner particles 101 (e.g., black) is held in toner supply hopper 102. Toner particles 101 are typically small plastic (e.g., styrene) particles on the order of 5 microns (10xe2x88x926 meters) in size. Agitator (or stirring blade) 103 is typically made of plastic, such as mylar, and ensures that toner particles 101 are uniformly positioned along developer roller 104 while inducing a negative charge onto the toner particles in the range of xe2x88x9230 to xe2x88x9280 micro-coulomb per gram (xcexcc/g). Developer roller 104 rotates in a counterclockwise direction about a shaft. Stationary magnet 105, internal to the developer roller assembly, attracts toner particles 101 to rotating developer roller 104 under influence of magnetic forces produced by stationary magnet 105. Doctor blade 106 charges the toner and metes out a precise and uniform amount of toner particles 101 onto developer roller 104 as its outer surface rotates external to toner supply hopper 102. As the outer surface of developer roller 104 rotates back into toner supply hopper 102 developer sealing blade 107 removes any excess toner particles 101 that are affixed to developer roller 104 because they did not transfer to OPC drum 109.
Primary Charging Roller (PCR) 108 conditions OPC drum 109 using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum 109 in the vicinity of PCR 108. Production of the uniform charge by PCR 108 also has the effect of erasing residual charges left from any previous printing or transfer cycle.
A critical component of the EP process is OPC drum 109. In a preferred embodiment, OPC drum 109 is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PCR 108. Initially, the unexposed surface potential of OPC drum 109 is charged to approximately xe2x88x92600 volts by PCR 108. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a Charge Transport Layer (CTL), Charge Generation Layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the underlying aluminum substrate.
Scanning laser beam 110 exposes OPC drum 109 one line at a time at the precise locations that are to receive toner (i.e., the paper locations that correspond to dark areas of the image being printed). OPC drum 109 is discharged from xe2x88x92600 V to approximately xe2x88x92100 V at points of exposure to laser beam 110, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles 101 are magnetically attracted to rotating developer roller 104. Alternatively, if a nonmagnetic toner is used, developer roller 104 may comprise a developer roller to mechanically capture and transport toner particles 101. In this case, an open cell foam roller may be included to apply toner to developer roller 104. The still negatively charged toner particles held by developer roller 104 are attracted to the relatively positively charged areas of the surface of OPC drum 109 and xe2x80x9cjumpxe2x80x9d across a small gap to the relatively positively charged latent image on OPC drum 109 creating a xe2x80x9cdevelopedxe2x80x9d image on the drum.
Blank paper to receive toner from OPC drum 109 is transported along paper path 111 between OPC drum 109 and transfer roller 112, with the developed image transferred from the surface of OPC drum 109 to the paper. The transfer occurs by action of transfer roller 112 which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles and causing them to move onto the paper. Wiper blade 113 cleans the surface of OPC drum 109 by scraping off the waste (untransferred) toner into waste hopper 115, while recovery blade 114 prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles, is passed through a nip region between heated roller 116 and pressure roller 117 where the toner is melted and fused (or xe2x80x9cbondedxe2x80x9d) to the paper. Heated roller 116 and pressure roller 117 are together referred to as the fuser assembly.
One design consideration with EP imaging devices, such as laser printers, is to minimize the leakage of toner from hopper 102. Leakage sometimes occurs at the ends of developer roller 104. Several methodologies and arrangements have been used to reduce or eliminate toner leakage from the ends of developer roller 104. Some printers employ a foam or felt mechanical seal at the ends of developer roller 104 as a physical barrier to prevent toner particles from slipping past the interface between developer roller 104 and toner supply hopper 102. Alternatively, when the toner includes magnetic properties, such as in many black and white printers, magnetic seals may be provided at the ends of developer roller 104 to attract monochromatic toner particles and create a physical barrier, consisting of the monochromatic toner particles, to prevent additional particles from leaking. Such techniques are generally inapplicable to the non-magnetic type of toner used, for example, in most color printers and copiers.
FIGS. 2 and 3 show other embodiments of a prior art developer roller/seal combinations. Support 202 positions seal 201 to ride on the surface portion of developer roller 204 within toner supply hopper 102 to limit toner migration past the seal and out of the hopper. In this arrangement, developer roller 204 interfaces directly with seal 201 in the area of reference point 302 and 303 (FIG. 3). Toner particles 101 are also present in the area of reference points 302 and 303, and the toner particles tend to build up in these areas adjacent seal 201. As developer roller 204 rotates in the direction indicated by arrow 304 (i.e., clockwise as viewed from the left end of developer roller 204), toner particles become lodged between developer roller 204 and seal 201. Toner particles 101 are pushed in a direction indicated by arrow 203. As developer roller 204 continues to rotate and additional toner particles become wedged in this interface, toner particles leak through seal 201. Seal leakage introduces toner into critical areas of the mechanism, thereby degrading performance, increasing maintenance requirements, and producing undesirable artifacts on the resultant printed paper or other product.
Accordingly, a need exists for a structure and method for reducing toner leakage in a toner cartridge.
The present invention is directed to a sealing mechanism for use in a toner cartridge comprising a developer roller having an outer cylindrical surface and a first plow including a concave contact region configured to mate with the outer cylindrical surface of the developer roller and a toner plow face placed at an acute angle with respect to a longitudinal axis of the developer roller.
Another embodiment of the present invention is directed to a method of reducing toner leakage in a toner cartridge comprising the steps of positioning a plow on an outer surface of a developer roller, rotating the developer roller and applying toner to the developer roller in a vicinity of the plow. In this embodiment, the plow pushes the toner in a direction away from an adjacent end of the roller, towards the middle of the roller.
Another embodiment of the present invention is directed to a toner cartridge comprising a housing, a development unit including a toner supply hopper and a developer roller having a cylindrical exterior surface. Also included in this embodiment is a cleaning unit including a waste hopper, a wiper blade, a cleaning blade and a blowout blade.
This latter embodiment also includes a primary charge roller, a transfer roller, an organic photo conductor and a pair of toner plows. The toner plows are integral to the housing, wherein each of the toner plows includes (i) a concave contact region configured to mate with the outer cylindrical surface of the developer roller and (ii) a toner plow face placed at an acute angle with respect to a longitudinal axis of the developer roller.